Isolation and culture of endothelial cells from the mesenteric vascular bed

Computational modeling of angiogenesis: The importance of cell rearrangements during vascular growth

Angiogenesis is the process wherein endothelial cells (ECs) form sprouts that elongate from the pre-existing vasculature to create new vascular networks. In addition to its essential role in normal development, angiogenesis plays a vital role in pathologies such as cancer, diabetes and atherosclerosis. Mathematical and computational modeling has contributed to unraveling its complexity. Many existing theoretical models of angiogenic sprouting are based on the "snail-trail" hypothesis. This framework assumes that leading ECs positioned at sprout tips migrate toward low-oxygen regions while other ECs in the sprout passively follow the leaders' trails and proliferate to maintain sprout integrity. However, experimental results indicate that, contrary to the snail-trail assumption, ECs exchange positions within developing vessels, and the elongation of sprouts is primarily driven by directed migration of ECs. The functional role of cell rearrangements remains unclear. This review of the theoretical modeling of angiogenesis is the first to focus on the phenomenon of cell mixing during early sprouting. We start by describing the biological processes that occur during early angiogenesis, such as phenotype specification, cell rearrangements and cell interactions with the microenvironment. Next, we provide an overview of various theoretical approaches that have been employed to model angiogenesis, with particular emphasis on recent in silico models that account for the phenomenon of cell mixing. Finally, we discuss when cell mixing should be incorporated into theoretical models and what essential modeling components such models should include in order to investigate its functional role. This article is categorized under: Cardiovascular Diseases > Computational Models Cancer > Computational Models.

Sympathetic Overactivity in CKD Disrupts Buffering of Neurotransmission by Endothelium-Derived Hyperpolarizing Factor and Enhances Vasoconstriction

BACKGROUND

Hypertension commonly complicates CKD. Vascular smooth muscle cells (VSMCs) of resistance arteries receive signals from the sympathetic nervous system that induce an endothelial cell (EC)-dependent anticontractile response that moderates vasoconstriction. However, the specific role of this pathway in the enhanced vasoconstriction in CKD is unknown.

METHODS

A mouse model of CKD hypertension generated with 5/6-nephrectomy (5/6Nx) was used to investigate the hypothesis that an impaired anticontractile mechanism enhances sympathetic vasoconstriction. In vivo, ex vivo (isolated mesenteric resistance arteries), and in vitro (VSMC and EC coculture) models demonstrated neurovascular transmission and its contribution to vascular resistance.

RESULTS

By 4 weeks, 5/6Nx mice (versus sham) had augmented increases in mesenteric vascular resistance and mean arterial pressure with carotid artery occlusion, accompanied by decreased connexin 43 (Cx43) expression at myoendothelial junctions (MEJs), impaired gap junction function, decreased EC-dependent hyperpolarization (EDH), and enhanced contractions. Exposure of VSMCs to NE for 24 hours in a vascular cell coculture decreased MEJ Cx43 expression and MEJ gap junction function. These changes preceded vascular structural changes evident only at week 8. Inhibition of central sympathetic outflow or transfection of Cx43 normalized neurovascular transmission and vasoconstriction in 5/6Nx mice.

CONCLUSIONS

5/6Nx mice have enhanced neurovascular transmission and vasoconstriction from an impaired EDH anticontractile component before vascular structural changes. These neurovascular changes depend on an enhanced sympathetic discharge that impairs the expression of Cx43 in gap junctions at MEJs, thereby interrupting EDH responses that normally moderate vascular tone. Dysregulation of neurovascular transmission may contribute to the development of hypertension in CKD.

Effects of endothelial cell proliferation and migration rates in a computational model of sprouting angiogenesis

Angiogenesis, the recruitment of new blood vessels, is a critical process for the growth, expansion, and metastatic dissemination of developing tumors. Three types of cells make up the new vasculature: tip cells, which migrate in response to gradients of vascular endothelial growth factor (VEGF), stalk cells, which proliferate and extend the vessels, and phalanx cells, which are quiescent and support the sprout. In this study we examine the contribution of tip cell migration rate and stalk cell proliferation rate on the formation of new vasculature. We calculate several vascular metrics, such as the number of vascular bifurcations per unit volume, vascular segment length per unit volume, and vascular tortuosity. These measurements predict that proliferation rate has a greater effect on the spread and extent of vascular growth compared to migration rate. Together, these findings provide strong implications for designing anti-angiogenic therapies that may differentially target endothelial cell proliferation and migration. Computational models can be used to predict optimal anti-angiogenic therapies in combination with other therapeutics to improve outcome.

The new antihypertensive drug iptakalim activates ATP-sensitive potassium channels in the endothelium of resistance blood vessels

AIM

To investigate the mechanisms underlying the activation of ATP-sensitive potassium channels (K(ATP)) by iptakalim in cultured rat mesenteric microvascular endothelial cells (MVECs).

METHODS

Whole-cell KATP currents were recorded in MVECs using automated patch clamp devices. Nucleotides (ATP, ADP and UDP) were added to the internal perfusion system, whereas other drugs were added to the cell suspension on NPC-1 borosilicate glass chips.

RESULTS

Application of iptakalim (10 and 100 μmol/L) significantly increased the whole-cell K(ATP) currents, which were prevented by the specific K(ATP) blocker glibenclamide (1.0 μmol/L). The opening of K(ATP) channels by iptakalim depended upon the intracellular concentrations of ATP or NDPs: iptakalim activated K(ATP) channels when the intracellular ATP or NDPs were at 100 or 1000 μmol/L, and was ineffective when the non-hydrolysable ATP analogue ATPγS (1000 μmol/L) was infused into the cells. In contrast, the K(ATP) opener pinacidil activated K(ATP) channels when the intracellular concentrations of ATP or NDPs ranged from 10 to 5000 μmol/L, and even ATPγS (1000 μmol/L) was infused into the cells.

CONCLUSION

Iptakalim activates K(ATP) channels in the endothelial cells of resistance blood vessels with a low metabolic status, and this activation is dependent on both ATP hydrolysis and ATP ligands.

Vascular and neural stem cells in the gut: do they need each other?

Enteric neurons and blood vessels form intricate networks throughout the gastrointestinal tract. To support the hypothesis of a possible interaction of both networks, we investigated whether primary mesenteric vascular cells (MVCs) and enteric nervous system (ENS)-derived cells (ENSc) depend on each other using two- and three-dimensional in vitro assays. In a confrontation assay, both cell types migrated in a target-oriented manner towards each other. The migration of MVCs was significantly increased when cultured in ENSc-conditioned medium. Co-cultures of ENSc with MVCs resulted in an improved ENSc proliferation and differentiation. Moreover, we analysed the formation of the vascular and nervous system in developing mice guts. It was found that the patterning of newly formed microvessels and neural stem cells, as confirmed by nestin and SOX2 stainings, is highly correlated in all parts of the developing gut. In particular in the distal colon, nestin/SOX2-positive cells were found in the tissues adjacent to the capillaries and in the capillaries themselves. Finally, in order to provide evidences for a mutual interaction between endothelial and neural cells, the vascular patterns of a RET((-/-)) knockout mouse model as well as human Hirschsprung's cases were analysed. In the distal colon of postnatal RET((-/-)) knockout mice, the vascular and neural networks were similarly disrupted. In aganglionic zones of Hirschsprung's patients, the microvascular density was significantly increased compared with the ganglionic zone within the submucosa. Taken together, these findings indicate a strong interaction between the enteric nervous and vascular system.

Exchange protein activated by cAMP (Epac) induces vascular relaxation by activating Ca2+-sensitive K+ channels in rat mesenteric artery

Vasodilator-induced elevation of intracellular cyclic AMP (cAMP) is a central mechanism governing arterial relaxation but is incompletely understood due to the diversity of cAMP effectors. Here we investigate the role of the novel cAMP effector exchange protein directly activated by cAMP (Epac) in mediating vasorelaxation in rat mesenteric arteries. In myography experiments, the Epac-selective cAMP analogue 8-pCPT-2-O-Me-cAMP-AM (5 μM, subsequently referred to as 8-pCPT-AM) elicited a 77.6 ± 7.1% relaxation of phenylephrine-contracted arteries over a 5 min period (mean ± SEM; n = 6). 8-pCPT-AM induced only a 16.7 ± 2.4% relaxation in arteries pre-contracted with high extracellular K(+) over the same time period (n = 10), suggesting that some of Epac's relaxant effect relies upon vascular cell hyperpolarization. This involves Ca(2+)-sensitive, large-conductance K(+) (BK(Ca)) channel opening as iberiotoxin (100 nM) significantly reduced the ability of 8-pCPT-AM to reverse phenylephrine-induced contraction (arteries relaxed by only 35.0 ± 8.5% over a 5 min exposure to 8-pCPT-AM, n = 5; P < 0.05). 8-pCPT-AM increased Ca(2+) spark frequency in Fluo-4-AM-loaded mesenteric myocytes from 0.045 ± 0.008 to 0.103 ± 0.022 sparks s(-1) μm(-1) (P < 0.05) and reversibly increased both the frequency (0.94 ± 0.25 to 2.30 ± 0.72 s(-1)) and amplitude (23.9 ± 3.3 to 35.8 ± 7.7 pA) of spontaneous transient outward currents (STOCs) recorded in isolated mesenteric myocytes (n = 7; P < 0.05). 8-pCPT-AM-activated STOCs were sensitive to iberiotoxin (100 nM) and to ryanodine (30 μM). Current clamp recordings of isolated myocytes showed a 7.9 ± 1.0 mV (n = 10) hyperpolarization in response to 8-pCPT-AM that was sensitive to iberiotoxin (n = 5). Endothelial disruption suppressed 8-pCPT-AM-mediated relaxation in phenylephrine-contracted arteries (24.8 ± 4.9% relaxation after 5 min of exposure, n = 5; P < 0.05), as did apamin and TRAM-34, blockers of Ca(2+)-sensitive, small- and intermediate-conductance K(+) (SK(Ca) and IK(Ca)) channels, respectively, and N(G)-nitro-L-arginine methyl ester, an inhibitor of nitric oxide synthase (NOS). In Fluo-4-AM-loaded mesenteric endothelial cells, 8-pCPT-AM induced a sustained increase in global Ca(2+). Our data suggest that Epac hyperpolarizes smooth muscle by (1) increasing localized Ca(2+) release from ryanodine receptors (Ca(2+) sparks) to activate BK(Ca) channels, and (2) endothelial-dependent mechanisms involving the activation of SK(Ca)/IK(Ca) channels and NOS. Epac-mediated smooth muscle hyperpolarization will limit Ca(2+) entry via voltage-sensitive Ca(2+) channels and represents a novel mechanism of arterial relaxation.

An in vitro model for spontaneous angiogenesis using rat mesenteric endothelial cells: possible therapeutic perspective for obesity and related disorders

CONTEXT

Abnormal obesity and the related diseases, such as diabetes and cardiovascular disease, are the main causes of mortality, around the world. A key feature of the adipogenesis and obesity is angiogenesis-dependent tissue growth accompanied with extracellular remodeling. In this way, suppression of angiogenesis may be a key point for preventing the adipogenesis.

OBJECTIVE

In the present study, to provide a deeper insight to understand obesity and screening for more effective therapeutics, we have developed a three-dimensional in vitro model of microvessel formation under collagen matrix culture using endothelial cells, extracted from a suitable tissue.

MATERIALS AND METHODS

In a successful approach for developing an angiogenesis model, the rat mesenteric microvascular endothelial cells (RMMECs) were isolated, coated on dextran beads and then suspended in collagen gel. Additionally, the proliferation as well as migration of endothelial cells were analyzed and compared with human umbilical vein endothelial cells (HUVECs).

RESULTS

RMMECs showed remarkable migration ability and had higher growth during the logarithmic growth phase, when compared with HUVECs. Also, no significance differences in morphogenesis were observed between HUVECs and RMMECs.

DISCUSSION AND CONCLUSION

The model may be useful in providing insights to develop potential intervention strategies in vivo against obesity-related disorders. Targeting endothelial cells is an interesting and exciting possibility that may be raised in further investigations.

Endothelial epithelial sodium channel inhibition activates endothelial nitric oxide synthase via phosphoinositide 3-kinase/Akt in small-diameter mesenteric arteries

Recent studies have shown that the epithelial sodium channel (ENaC) is expressed in vascular tissue. However, the role that ENaC may play in the responses to vasoconstrictors and NO production has yet to be addressed. In this study, the contractile responses of perfused pressurized small-diameter rat mesenteric arteries to phenylephrine and serotonin were reduced by ENaC blockade with amiloride (75.1+/-3.2% and 16.9+/-2.3% of control values, respectively; P<0.01) that was dose dependent (EC(50)=88.9+/-1.6 nmol/L). Incubation with benzamil, another ENaC blocker, had similar effects. alpha, beta, and gamma ENaC were identified in small-diameter rat mesenteric arteries using RT-PCR and Western blot with specific antibodies. In situ hybridization and immunohistochemistry localized ENaC expression to the tunica media and endothelium of small-diameter rat mesenteric arteries. Patch-clamp experiments demonstrated that primary cultures of mesenteric artery endothelial cells expressed amiloride-sensitive sodium currents. Mechanical ablation of the endothelium or inhibition of eNOS with N(omega)-nitro-L-arginine inhibited the reduction in contractility caused by ENaC blockers. ENaC inhibitors increased eNOS phosphorylation (Ser 1177) and Akt phosphorylation (Ser 473). The presence of the phosphoinositide 3-kinase inhibitor LY294002 blunted Akt phosphorylation and eNOS phosphorylation and the decrease in the response to phenylephrine caused by blockers of ENaC, indicating that the phosphoinositide 3-kinase/Akt pathway was activated after ENaC inhibition. Finally, we observed that the effects of blockers of ENaC were flow dependent and that the vasodilatory response to shear stress was enhanced by ENaC blockade. Our results identify a previously unappreciated role for ENaC as a negative modulator of eNOS and NO production in resistance arteries.

Erythropoietin stimulates vasculogenesis in neonatal rat mesenteric microvascular endothelial cells

Human breast milk is a rich source of growth factors, including erythropoietin (Epo), the endogenous hormonal stimulant of erythropoiesis. Recombinant human Epo (rhEpo) has been shown to stimulate 1) angiogenesis, the process of new blood vessel growth from preexisting vessels; 2) vasculogenesis, tubule formation from single-cell suspensions; and 3) endothelial cell proliferation in immortalized endothelial cells and vessel explants. We hypothesized that Epo would induce mitogenesis and stimulate vasculogenesis in primary cultures of microvascular endothelial cells (MVECs) from neonatal rat mesentery. Isolation, purification, characterization, and culture of MVECs were performed. Cell proliferative effects of rhEpo were studied by 3-(4,5 dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay in cultured MVECs. Vasculogenic effects of rhEpo were examined on cultured MVECs plated on either hormone-rich Matrigel substratum or the extracellular matrix protein, type I collagen. Our findings show that MVECs are isolated and purified, and that rhEpo stimulates MVEC proliferation, with maximal proliferation seen with a concentration of 50 IU/mL rhEpo. Tubule formation assays reveal that an rhEpo concentration of 50 IU/mL produces maximal tubule formation after 12 h on both Matrigel and the simple substratum, type I collagen. Our study is the first to examine the effects of rhEpo on the endothelium of the neonatal gastrointestinal tract. These data suggest that Epo may have a trophic effect on the vasculature of the gastrointestinal tract early in development. Furthermore, as Epo has been measured in breast milk, and its receptor has been shown to exist on the mucosa and gastrointestinal vasculature, Epo may be an endogenous stimulant of vessel growth during neonatal gastrointestinal development.